The invention relates to the fabrication of superconductors. More particularly, the invention relates to the fabrication of continuous lengths of superconductors having at least one superconducting oxide layer between metallic substrates.
The quality of the interface layer between a superconducting material and a metallic substrate is very important in superconducting oxide/metal conductors. The densest and most highly textured superconducting oxide is generally at the interface between the superconducting oxide and the metallic substrate. Consequently, the interface must be smooth, and in tape geometries, planar.
Preparation of long lengths of superconductor is especially difficult. The powder-in-tube method has been previously utilized with some success. Additionally, recent processes include the utilization of multilayered foils coated with superconductor precursor powders that are sealed in a box and unidirectionally rolled. These, and other, methods for preparing long lengths of a super conductor result in interfaces between the superconducting material and the substrate that are less than ideal.
Specifically, fabrication processes such as the powder-in-tube method produce long conductor lengths by starting with large billets containing oxide cores several millimeters or more in diameter. Dimensional uniformity of the core and a smooth interface are difficult to maintain during the large reduction in cross section necessary for fabrication of long thin ribbon conductors.
U.S. Pat. No. 5,034,272 to Matsuno et al. and U.S. Pat. No. 5,002,928 to Fukio et al. describe methods for depositing oxide substances on substrates to form superconductors. Both methods include the deposition of atomized superconductive oxide substances onto a substrate.
Additionally, Shiga et al. (U.S. Pat. No. 5,104,849) describes the manufacture of an oxide superconductor wire. The wire is manufactured by applying oxide powder to cylindrical stabilizing metal materials having differing diameters. The coated metal materials are then concentrically arranged. The wire is rolled, before heating the same to produce the oxide superconducting wire. Other superconductors and methods for manufacturing superconductors are disclosed in U.S. Pat. No. 5,208,215 to Chen et al., U.S. Pat. No. 5,187,149 to Jin et al., U.S. Pat. No. 5,164,360 to Woolf et al., U.S. Pat. No. 5,151,406 to Sawanda et al., and U.S. Pat. No. 5,059,582 to Chung.
The prior art discussed above neither discloses nor suggests the present process or apparatus for manufacturing continuous strips of superconducting materials having a smooth interface between the superconducting material and the substrate. Additionally, the prior art does not disclose or suggest a superconductor manufactured by the present process. The present process reduces the deformation normally resulting from the rolling and drawing utilized by the prior art methods, thus yielding improved texture and less roughness at the interface between the substrate and the superconducting film.
An object of the invention is to provide long lengths of superconductor and a process for preparing the same.
Another object of the invention is to provide a method for the preparation of long lengths of superconductor having a superior interface between the superconducting material and the metal substrate.
A further object of the invention is to provide a process and apparatus for manufacturing long lengths of superconductor having very good dimensional stability.
These and other objects of the present invention are achieved by the present process for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor comprising a layer of said superconducting precursor powder between said first substrate ribbon and said second substrates ribbon. The layered superconductor is then heat treated to establish the superconducting phase of said superconductor precursor powder.
The limited fabrication required by the present invention results in improved homogeneity. Specifically, the present invention only relies upon a two fold reduction in the thickness of the superconductor during the fabrication thereof. The homogeniety produced by the present invention results in a superconductor having better electrical characteristics than those demonstrated by prior art superconductors. Additionally, superconductors made in accordance with the present invention demonstrate an absence of non-superconducting materials at the interface and improved dimensional stability.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description which, taken in conjunction with the annexed drawings, discloses the preferred embodiment of the subject invention.